A more thorough explanation:

Definition: Double wills are two similar wills created by two individuals with the intention of each person receiving the assets of the other if they die first. There are two types of double wills: mutual wills and reciprocal wills.

Mutual wills are double wills where two individuals agree that the survivor cannot change their will after the other dies. This means that the inheritors specified in the document cannot be changed after one person dies, binding both individuals to the wills. The wills can be changed before one of the two individuals die with adequate notice to the other party. If one tries to create a mutual will, some states require an explicit agreement that the wills were meant to be irrevocable after the death of one of the parties, but in others, an oral agreement may suffice. The surviving individual cannot attempt to go around this limitation by gifting away assets allocated in the will inter vivos either.

John and Jane are married and have two children. They create mutual wills that state that if one of them dies, the other will receive all of their assets. They also agree that after one of them dies, the survivor cannot change the will. This means that if John dies first, Jane will receive all of his assets, and she cannot change the will to exclude their children.

Reciprocal wills are not mutual wills because if one of the individuals dies, the other can still change their will. The main point of reciprocal wills is that each spouse agrees that the other receives the entirety of their assets upon death.

Tom and Sarah are married and have no children. They create reciprocal wills that state that if one of them dies, the other will receive all of their assets. However, if Tom dies first, Sarah can change her will to exclude Tom's family members from receiving any of her assets.

These examples illustrate the concept of double wills and the differences between mutual and reciprocal wills. Mutual wills are more binding because the survivor cannot change the will after the other dies, while reciprocal wills allow for more flexibility.